1. Field of the Invention
The present invention is directed to a light control device for deflecting light at high speeds or for changing a light focusing position at high speeds. The control device may be used, for example, in a laser printer or in an optical disk device.
2. Description of the Background Art
Some conventional light control devices (EO devices) take advantage of an electro-optical effect whereby the refractive index of a transparent medium is altered by applying an electric field to the transparent medium. These devices may be of a first type wherein light is directed through an electro-optical material, or of a second type wherein light is directed through a waveguide layer formed on an electro-optical material.
FIG. 2 is an explanatory view of a light control device of the first type mentioned above.
In FIG. 2, an electro-optical material 2 is formed in the shape of a triangular prism having a thickness d (mm). Electrodes 7 and 8 are provided to completely cover opposite major surfaces of the electro-optical material 2.
When a voltage is applied to the electrodes 7 and 8, an electric field is generated between the electrodes within the electro-optical material 2. Ingoing light 9 is applied to the prism 7, and outgoing light 10 is deflected by the electric field.
FIG. 3 is an explanatory view of a light control device of the second type mentioned above.
In FIG. 3, a waveguide layer 40 is provided on an upper major surface of the electro-optical material 2. Electrodes 41 and 42 are formed on an exposed surface of the waveguide layer 40. When a voltage is applied between the electrodes 41 and 42, an electric field is generated along the exposed surface of the waveguide layer 40, so that light passing between the electrodes is deflected. A diffraction grating may be used instead of the prism 1 for directing light 9 into the waveguide layer 40.
In the light control device of the first type (FIG. 2), in order to produce a large deflection of the outgoing light 10, the electric field must be increased and the beam diameter D of the incoming light 9 must also be increased. Further, in order to obtain a large electric field with a small applied voltage, the thickness d of the electro-optical material 2 must be reduced.
Thus, in order to produce a large deflection of the outgoing light 10 in the light control device of the first type, a transversely-extended, oval shaped light must be made to enter an electro-optical material having a relatively small thickness d. However, it is difficult to realize the configuration. Furthermore, in order to produce a large deflection of the outgoing light 10 in the light control device of the second type (FIG. 3), the electric field intensity must be increased and the width of the light D must be increased. In order to increase the electric field intensity, it is desirable to decrease the interval d between electrodes 41, 41, thereby decreasing the distance between the electrodes 41, 42. However, when the width of the light D is increased, the electrode interval d should also be increased. Consequently, in the light control device of the second type (FIG. 3), it is difficult to produce a large deflection of the light.